🎮 GPU Passthrough + Looking Glass Guide

This guide explains how to set up a Windows VM with GPU passthrough and Looking Glass on Ubuntu 25.04.

Prerequisites

• CPU with VT-d/AMD-Vi enabled in BIOS:

  lscpu | grep "Virtualization"
  Virtualization: VT-x   # Intel
  Virtualization: AMD-V  # AMD
  

• Two GPUs (one for Linux, one for the VM):

  lspci -nn | grep VGA
  00:02.0 VGA compatible controller [0300]: Intel Corporation Meteor Lake-P [Intel Arc Graphics] [8086:7d55] (rev 08)
  01:00.0 VGA compatible controller [0300]: NVIDIA Corporation AD106M [GeForce RTX 4070 Max-Q / Mobile] [10de:2820] (rev a1)
  

  Note the IDs in square brackets for the GPU you want to passthrough — in this case: 10de:2820.

• Two audio controllers:

  lspci -nn | grep -i audio
  00:1f.3 Multimedia audio controller [0401]: Intel Corporation Meteor Lake-P HD Audio Controller [8086:7e28] (rev 20)
  01:00.1 Audio device [0403]: NVIDIA Corporation AD106M High Definition Audio Controller [10de:22bd] (rev a1)
  

  Again, note the IDs — in this case: 10de:22bd.

• HDMI Dummy Plug (optional): helpful for Looking Glass to trick the guest GPU into enabling display output.

Isolating your GPU

Install QEMU/KVM

QEMU is an open-source hypervisor that works with KVM to take advantage of hardware acceleration.

sudo apt update
sudo apt install qemu-kvm virt-manager bridge-utils linux-headers-$(uname -r) dkms
sudo reboot now

Enable libvirtd and add your user to the libvirt group:

sudo systemctl enable libvirtd.service
sudo systemctl start libvirtd.service
sudo usermod -aG libvirt $USER

Enable IOMMU in GRUB

IOMMU (Input-Output Memory Management Unit) is required to isolate and assign hardware devices to VMs securely.

Edit the GRUB configuration to enable IOMMU and specify the device IDs:

sudo vim /etc/default/grub

For Intel CPUs:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash intel_iommu=on iommu=pt vfio-pci.ids=10de:2820,10de:22bd"

For AMD CPUs, replace intel_iommu=on with amd_iommu=on.

Update GRUB:

sudo grub-mkconfig -o /boot/grub/grub.cfg
sudo reboot now

Bind the GPU to VFIO

VFIO allows direct and secure assignment of devices to VMs.

Create the config:

sudo vim /etc/modprobe.d/vfio.conf

Add:

options vfio-pci ids=10de:2820,10de:22bd

Blacklist other drivers to prevent them from binding to the GPU:

sudo tee /etc/modprobe.d/blacklist-nvidia.conf > /dev/null <<EOF
blacklist nouveau
blacklist nvidia
blacklist nvidiafb
blacklist rivafb
blacklist nvidia_drm
blacklist nvidia_uvm
blacklist nvidia_modeset
EOF

Update the initramfs:

sudo update-initramfs -c -k $(uname -r)

Enable DMA GPU transfers (Looking Glass)

IVSHMEM (Inter-VM Shared Memory) is a QEMU feature allowing memory segments to be shared between the host and guest. Looking Glass uses it to facilitate high-speed, low-latency frame sharing via DMA (Direct Memory Access).

Download the Looking Glass source: https://looking-glass.io/artifact/B7/source

Extract the archive and navigate to the module/ directory:

cd looking-glass-B7/module

Install the kernel module:

dkms install .

Create /etc/modprobe.d/kvmfr.conf:

options kvmfr static_size_mb=128

Create /etc/modules-load.d/kvmfr.conf:

kvmfr

Create a udev rule to allow your user access to /dev/kvmfr0 (replace user with your username):

sudo tee /etc/udev/rules.d/99-kvmfr.rules > /dev/null <<EOF
SUBSYSTEM=="kvmfr", OWNER="user", GROUP="kvm", MODE="0660"
EOF

Verify GPU Isolation

Reboot and verify

Run:

lspci -k | grep -E "Audio|VGA|vfio-pci"

Expected output:

01:00.0 VGA compatible controller: NVIDIA Corporation AD106M [...]
    Kernel driver in use: vfio-pci
01:00.1 Audio device: NVIDIA Corporation AD106M High Definition Audio [...]
    Kernel driver in use: vfio-pci

vfio-pci should be listed as the kernel driver in use.

You should now also have the character device /dev/kvmfr0

ls -l /dev/kvmfr0

Expected:

crw------- 1 user kvm 242, 0 Jun 16 12:00 /dev/kvmfr0

Create your dedicated gaming VM

Download the Windows ISO

Get a copy of Windows from:

• Windows 10
• Windows 11

Download the virtio-win ISO from the official repository

and move all ISO to /var/lib/libvirt/images/

sudo chown libvirt-qemu:kvm /var/lib/libvirt/images/*.iso

Launch the VM with virt-install

sudo virt-install --name=Win10-gaming --vcpus=8 --memory=16384 --os-variant=win10 --features kvm_hidden=on --machine q35 --cdrom=/var/lib/libvirt/images/Win10_22H2_French_x64v1.iso --disk path=/var/lib/libvirt/images/win10.qcow2,size=100,bus=virtio,format=qcow2 --disk path=/var/lib/libvirt/images/virtio-win-0.1.271.iso,device=cdrom,bus=sata --graphics spice,listen=127.0.0.1 --video virtio --network network=default,model=virtio --hostdev pci_0000_01_00_0 --hostdev pci_0000_01_00_1 --wait -1

Command details

Install Windows

Use SPICE to connect and install Windows:

virt-viewer Win10-gaming

During installation:

• Browse to the VirtIO drive to load storage drivers when prompted.

Install Drivers

Once inside Windows:

• Run virtio-win-guest-tools.exe from the VirtIO ISO.
• Install GPU drivers: Nvidia, AMD, or Intel.

Install LookingGlass

Looking Glass is an open source application that allows the use of a KVM (Kernel-based Virtual Machine) configured for VGA PCI Pass-through without an attached physical monitor, keyboard or mouse.

On your VM, install Windows binary from https://looking-glass.io/artifact/B7/host

On your host, install the application client

mkdir host/build
cd host/build
cmake ..
make
make install

Tune the VM

To optimize performance, edit the XML:

<cpu mode='host-passthrough' check='none' migratable='on'>
    <topology sockets='1' dies='1' clusters='1' cores='4' threads='2'/>
    <maxphysaddr mode='passthrough' limit='40'/>
    <feature policy='disable' name='hypervisor'/>
</cpu>

Modifying the XML domain namespace to support qemu:commandline block

  <qemu:commandline>
    <qemu:arg value='-device'/>
    <qemu:arg value='ivshmem-plain,id=shmem0,memdev=looking-glass,bus=pcie.0,addr=0x11'/>
    <qemu:arg value='-object'/>
    <qemu:arg value='memory-backend-file,id=looking-glass,mem-path=/dev/kvmfr0,size=128M,share=yes'/>
  </qemu:commandline>